Production and transportation of oil and natural gas generally involves transporting the oil and gas along various types of channel housing. For example, during conventional oil and gas production, oil and gas are pumped out of a formation via production tubing that has been laid along a wellbore; in this example, the production tubing is the channel housing. Similarly, when hydraulic fracturing is used to produce oil and gas, the well in which the fracking is performed is the channel. As another example, oil and gas, whether refined or not, can be transported along a pipeline; in this example, the pipeline is the channel housing. In each of these examples, acoustic events may occur within the channel housing that are relevant to oil and gas production or transportation. For example, the pipeline or the production tubing may be leaking, and during fracking new fractures may be formed and existing fractures may expand. Each such event is an acoustic event as it makes a noise while it is occurring. Fibre optic cables can be deployed downhole for the detection of acoustic events in channel housing used for the production and transportation of oil and gas.
Fluid migration in oil or gas wells is generally referred to as “casing vent flow” (CVF) or “gas migration” (GM) and can refer to any one or more of the following phenomena:                Fluid flowing from the formation into an outermost annular portion of the wellbore behind an outermost casing string in the wellbore;        Fluid flowing from the outermost annular portion of the wellbore into the formation; and        Fluid flowing across any of the casing or tubing strings in the wellbore.        
Fluid includes gas or liquid hydrocarbons, including oil, as well as water, steam, or a combination thereof. Any fluid migration will produce an “acoustic signal”. Acoustic signals resulting from the migration of fluid may be used as an identifier, or “diagnostic”, of a leaking well. For example, gas may migrate as a bubble from the source up towards the surface, frequently taking a convoluted path that may progress into and/or out of the production casing, the surrounding earth strata and the cement casing of the wellbore, and may exit into the atmosphere through a vent in the well, or through the ground. As the bubble migrates, pressure may change and the bubble may expand or contract and may increase or decrease its rate of migration and produce an acoustic event.
Acoustic signals may also be used to detect fluid leaking from a pipeline, tubular, riser or the like transporting fluid such as oil or gas. The acoustic signature is analyzed for deviations from the baseline flow. Depending on the type of fluid being transported in a channel, a fluid leak may have a particular acoustic signature (e.g. high frequency, louder than usual acoustic magnitude, etc). Using software algorithms, an operator can analyze this acoustic signature and detect fluid leaks in the pipeline.
Fibre optic cables may also be deployed in vessels for storing a fluid and used to detect acoustic signals indicative of fluid leaking from the vessel.